Method of stiffening the corrugations of corrugated cardboards and the resultant prodct



3,357,877 ATED Dec. 12, 1967 GANDON METHOD OF STIFFENING THECORRUGATIONS OF CORRUG CARDBOARDS AND THE RESULTANT PRODUCT Filed Jan1964 United States Patent 9 Claims. Cl. 161-133) The present inventionhas for its object a method of stiffening the corrugations of corrugatedcardboards, said method being characterized essentially by the treatmentof the papers to be corrugated with an aqueous solution of glyoxalcontaining guar gum and a condensation catalyst.

In order to make the nature of the present invention more clearlyunderstood, there will first be described the mechanical aspect of itsexecution, this aspect being shown diagrammatically by the accompanyingdrawings.

FIG. 1 shows a corrugated cardboard which comprises a corrugated paper 1known as a corrugation or wave on each face of which is stuck anon-corrugated paper, namely the outer cover 2 and the inner cover 3.During the manufacture of a cardboard box, the said covers are locatedon the outside and on the inside of the box, respectively.

In a composite cardboard of this kind, the part which is at the sametime the most important and the most difficult to produce is the rigidcorrugation. This corrugation, although made of paper, must in fact havesufilcient resistance to crushing when laid flat so that it can beemployed for the manufacture of boxes or cases of corrugated cardboardused for packing articles of the most varied kinds.

Corrugated cardboards used in practice for the manufacture of suchpacking cases may be either simpler or more complex than that shown inFIG. 1, which is known as double corrugated cardboard, but they allcomprise the said rigid corrugation and at least one covering sheetstuck on it, it being always essential for the corrugation to have themaximum strength to crushing when flat. Thus, there are also used forexample simple corrugated cardboardsf (comprising but one corrugationand one cover); double-double corrugated cardboards (comprising an outercover, a small corrugation, a central corrugation, a large corrugationand an inner cover); triple corrugated cardboards, etc.

For the manufacture of a simple corrugated cardboard according to themethod of the present invention, the

mechanical operative-steps shown diagrammatically in FIG. 2 willpreferably be carried out: a sheet of paper supplied from a roll 4 ofstraw-paper for example, moving forward at a uniform speed in thedirection of arrow 5, is wetted at 6 with the said aqueous solution ofglyoxal containing guar gum and a condensation catalyst. The sheet ofpaper then passes over a heating drum 7 and then between two corrugatingcylinders 8 (toothed wheels). The heating produces a thermalplastification (as in the case of a permanent wave) and the paper comesout in the corrugated state after passing between the two cylinders.

The said corrugated rigid paper (corrugation) passes over a cylinder 9rotating in a bath of an adhesive agent 10; it is then coated with thesaid adhesive (of silicate for example) and finally during its passageover a heating drum 11 meets the sheet of paper which is to serve as acover, supplied from a roll 12 of paper; the cover sheet is thus stuckon the corrugation, the heating at 11 accelerating the setting of theadhesive agent.

It will be understood without further explanation that by the sameprocess it is possible to stick a second cover sheet on the other faceof the corrugation, or alternatively to manufacture double-double ortriple corrugated cardboards, etc.

The mechanical process having thus been explained, the nature of theinvention will be illustrated in a more detailed manner.

In known methods, water is generally used for the impregnation of thepaper to be treated. There is thus obtained a corrugation whoseresistance to crushing when flat (which is a measure of the stiffness)is fair, but which, in the damp state, has only a quite poor rigidity orstiffness, which is a great practical drawback. In fact, corrugatedcardboard boxes manufactured with such corrugations cannot be employedas packings for certain kinds of food products, such as fruit,vegetable, etc., which breathe, that is to say which create anatmosphere saturated with moisture. Under the action of humidity, theresistance to crushing of the corrugations falls to an insufiicientvalue and the packing of corrugated cardboard collapses, which makes itunsuitable for this kind of use. The problem of behaviour to moisturealso presents itself for example during transport over long distances bysea.

Now, the production of a cheap packing material for such uses in thefield of corrugated cardboards meets at the present time a pressing needin the industry.

The known methods for improving the resistance to water of papers suchas those which serve as cover sheets in the manufacture of corrugatedcardboard, do not provide any solution to the problem as set hereabove.In fact, it is the central corrugation of the corrugated cardboard whichmust have the requested properties of stiffness and resistance to water;the properties of the cover sheets being of minor importance; inaddition, it is necessary to have a simple and inexpensive method which,furthermore, should neither modify nor complicate existinginstallations.

The products generally employed for sufiiciently improving themechanical properties of paper (e.g. thermosetting resins) are notsuitable in this case since paper pre-treated with such products has nothermo-plasticity and breaks when it passes between the two corrugatingcylinders 8.

An attempt has been made to cope with this drawback by the use ofthermo-plastic resins, more particularly polydiene resins, for the priorimpregnation of the paper to be corrugated. However, such a method isnot applicable in practice on a large scale. On the one hand, thenecessity of utilizing a volatile organic solvent in order to distributethe resin uniformly in the paper, is already prohibitive, by reason ofthe large quantities of solvent which are liberated in the workshop orwhich have to be recovered by the use of complex and expensiveinstallations; on the other hand, a paper treated in this way does notaccept, when applied at the cylinder 9, enough of the usual adhesiveagents intended to stick the cover sheet on the corrugation; it would benecessary to use special and costly adhesive agents under complicatedconditions of use. The method of the present invention replaces atwetting position 6 the moistening water generally use, by an aqueoussolution of glyoxal containing guar gum and a condensation catalyst;this method makes it possible to obtain, without in any way modifyingexisting installations, a considerable improvement in the resistance tocrushing of the corrugations, both in the dry state and in the wetstate.

For carrying out the method according to the invention the paper to betreated is impregnated with the said solution so that the quantity ofsolution retained by the paper corresponds to a weight of from 0.5 gramto about if: 10 grams of dry material deposited per square metre ofpaper, for example from 1 to 5 grams; then, the thus treated paper isconverted to a rigid corrugation, preferably in the manner indicatedabove, which is shown diagrammatically in FIG. 2.

The preferred sequence of the operations is therefore as follows, in thecase of a simple corrugated cardboard: impregnation of the paper by thesaid solution at wetting position 6 according to the invention;thermo-plastification by heaing such as with the heating drum 7;corrugation steps, such as deformation with the cylinders 8; coating atcylinder 9 with an adhesive agent and applying the cover sheet such aswith the drum 11.

The temperature employed for the thermo-plastification has no influencewhatever on the results which can be obtained by the present method,since the useful reaction already takes place when cold; it is thuspossible to work at the usual temperatures of practice already adoptedby the various factories already in operation.

Without departing from the scope of the invention, any other mechanicalprocess of conversion of the impregnated paper to a rigid corrugationcan be employed.

The aqueous solution to be used for the impregnation of the paper to betreated comprises, per litre, preferably between 20 and 200 grams ofglyoxal expressed in CHO-CHO and, with respect to the glyoxal,preferably from about 10 to 50% by weight of dry guar gum and from about2 to 8% of condensation catalyst.

For the preparation of the said solution, glyoxal may be employed in theform of an aqueous solution, or alternatively in the form of glyoxalpolyhydrate in powder form.

The guar gum, which is a galacto-mannite gum chemically constituted ofunits of galactose and mannose, can be dissolved in the form of powderor after having been previously brought into the form of an aqueoussolution. The various commercial kinds of guar gums can be employed, inparticular the one having a very low viscosity (50 cp. at C., in a 2%solution).

The condensation catalysts to be employed are preferably acidiccompounds or such as are capable of producing acids during the course ofthe treatment, such as the chlorides or sulphates of non-alkalinemetals, for ex ample aluminum sulphate.

The order in which the various compounds are dissolved has no influencewhatever on the results.

There may also be prepared a mixture of powders constituted by glyoxalpolyhydrate, guar gum and the sulphate. There are added 200 grams of dryguar gum of very low viscosity cp. at 20 C. in a 2% solution).

This mixture is made-up to a volume of 10 litres with water, and thenstirred until the solution is complete, which gives a perfectly clearsolution.

A straw-paper having a weight of 140 grams per square metre isimpregnated with the said solution, in such manner that the amount ofsolution retained by the paper corresponds to n grams of dry materialdeposited per square metre of paper.

Three operations a, b, 0, have been carried out in this way so as todeposit in the three cases the following quantities of dry material persquare metre of paper:

Operation a: 11:1 g. Operation b: 12:33 g. Operation 0: n=4.8 g.

The impregnated papers are converted to rigid corrugations in the mannerdescribed in the present specification diagrammatically shown in FIG. 2.

In order to appreciate the qualities of the corresponding rigidcorrugations, a sample of each of the three papers a, b and c wassubjected to the standard test of the ring crush according to thestandard of the T.A.P.P.I. (Technical Application Pulp and PaperIndustry) 472 m 51, which provides a figure expressing the annularstiffness in lbs/inches, which stiffness represents the 0thcial test ofresistance to crushing.

On each of the papers, test-pieces were taken in the machine directionand test-pieces in the cross direction; in each case, the measurementswere made, on the one hand, on the dry paper and on the other hand onthe wet paper. The dry paper is a paper conditioned for 24 hours in anatmosphere of relative humidity at 20 C., the wet paper was prepared byprevious conditioning for 48 hours in an atmosphere having 90% relativehumidity at 20 C.

An untreated paper, called a check-sample was examined under strictlyidentical conditions.

After having measured the resistances to crushing, the coefficients werecalculated, that is to say the ratios of the resistances of the treatedpapers to the resistance of the corresponding sample paper.

Finally, the ratios wet/dry or W/D were calculated, that is to say theresistances to crushing of the wet papers, divided by the resistance tocrushing of the corresponding dry check-sample, in percent.

The following results were obtained:

TABLE I Resistances to crushing Coefiicients Ratio W/D n Machine CrossMachine Cross (gJmfi) direction direction direction direction giaclzined Cross irec ion irection Dry Wet Dry Wet Dry Wet Dry Wet (percent)(percent) paper paper paper paper paper paper paper paper Cheek sample38 14 25 6 37 24 Operation ((1) 1 50 23 27 8. 2 1.32 1. 64 1.08 1.37Operation (b).. 3.3 50 31 32 17 1.32 2. 32 1.28 2. 84 2% Operation (0)4. 8 58 32 43 20 1. 53 2. 28 1. 72 3.84 84 80 catalyst. This product inpowder form can be stored, transported, etc.; it will be put into anaqueous solution for carrying out the method according to the invention.

In order to make the invention more clearly understood, there will begiven below, by way of illustration but without any limitation, a fewexamples of the method of execution and the results which can beobtained.

Example 1 In 5,000 grams of an aqueous solution of glyoxal at 30% byweight, there are dissolved 75 grams of aluminum Example 2 50 grams ofaluminum sulphate is dissolved in 3,300 grams of an aqueous solution ofglyoxal at 30% by weight. There is added 200 grams of dry guar gumhaving the following amounts of dry material per square metre of paper:

Operation a": n=1 gram Operation b": w=3fl grams a very low viscosity. 5(See the table which follows.)

TABLE III [Results: 'I=check sample] Resistances to crushingOoeificients Ratio W/D 11 Machine Cross Machine Cross (gJmfi) 2direction direction direction direction Machine Cross directiondirection Dry Wet Dry Wet Dry Wet Dry Wet (percent) (percent) paperpaper paper paper paper paper paper paper Operation a: n=l gramOperation b: n=2.5 grams Operation c: n=4.7 grams By way of comparison,an operation E was made with a solution identical to the preceding one,but containing glyoxal and the catalyst only, and therefore no guar gum(3,300 grams of 30% glyoxal solution+50 grams of aluminum sulphate in 10litres) described in the following table:

TABLE II The above examples have been given with guar gum, but obviouslyother galacto-mannites may be used such as, for instance, carob-gum.

I claim:

1. A paper impregnating and coating composition of matter consistingessentially of 10 parts by weight glyoxal, 1-5 parts by Weight guar gumand an acidic condensation catalyst selected from the group consistingof non-alkaline metal chlorides and sulfates.

2. A paper impregnating and coating composition consisting essentiallyof an aqueous solution containing from 20 to 200 grams per litre ofglyoxal expressed as CHO-CI-I'O and, on the basis of the weight ofglyoxal, from 10 to of dry guar gum and from 2 to 8% of an acidiccondensation catalyst selected from the group consisting of non-alkalinemetal chlorides and sulfates.

[Results (T=check samp1e)] Resistances to crushing Coefiicients RatioW/D n Machine Cross Machine Cross (gJmfl) direction direction directiondirection Machine Cross direction direction Dry Wet Dry Wet Dry Wet DryWet (percent) (percent) paper paper paper paper paper paper paper paperIt is seen that the resistances to crushing of the papers reach valuesmore than double and even more than three times those of thecorresponding untreated papers and that the resistances to crushing ofwet papers reach values close to or equal to that of the correspondingcheck sample of dry paper, which is remarkable.

It can also be seen that under the conditions of the present invention,the glyoxal with the catalyst alone, in the absence of guar gum, givespractically no improvement in the resistance'to crushing, either in thedry or in the wet states.

Example 3 In 1660 grams of an aqueous solution of glyoxal at 30% byweight, there are dissolved 25 grams of aluminum sulphate. There isadded 200 grams of dry guar gum having a very low viscosity.

The mixture is completed to a volume of 10 litres with water and thenstirred until everything is completely dissolved.

The procedure is continued as in Example 1, carrying out two operations,a" and b in such manner as to deposit the impregnated sheet, and heatingthe resulting corrugated paper, the improvement which comprises carryingout said impregnating and coating step using a composition consistingessentially of 10 parts by weight glyoxal, 1-5 parts by weight guar gumand an acidic condensation catalyst selected from the group consistingof non-alkaline metal chlorides and sulfates.

5. The improvement according to claim 4 wherein the amount of saidimpregnating and coating composition applied to said paper is from 0.5to 10 grams on a dry basis per square metre of paper.

6. A composition in accordance with claim' 2 wherein said acidiccondensation catalyst is aluminum sulfate.

7. A method in accordance with claim 5 wherein the amount of saidcomposition applied, on a dry basis, is between 1 and 5 grams per sq.metre of paper.

8. A corrugated paper of high wet strength comprising paper impregnatedwith a composition consisting essentially of 10 parts by weight glyoxal,1-5 parts by weight guar gum and an acidic condensation catalystselected from the group consisting of non-alkaline metal chlorides andsulfates.

9. A corrugated paper in accordance with claim 8 wherein said impregnantcomposition comprises 0.5 to 10 grams per square metre of paper and theamount of the catalyst comprises 2 to 8% catalyst based on the weight ofglyoxal.

References Cited UNITED STATES PATENTS 1,796,542 3/1931 Schoo 161-1372,568,349 9/1951 McKee 161-137 2,644,750 7/1953 Frisch et a1 1062053,228,928 1/1966 Opie et al 106205 3,276,885 10/1966 Gandon 106208FOREIGN PATENTS 1,356,282 2/ 1964 France.

MORRIS SUSSMAN, Primary Examiner.

8. A CORRUGATED PPER OF HIGH WET STRENGTH COMPRISING PAPER IMPREGNATEDWITH A COMPOSITION CONSISTING ESSENTIALLY OF 10 PARTS BY WEIGHT GLYOXAL,1-5 PARTS BY WEIGHT GUAR GUM AND AN ACIDIC CONDENSATION CATALYSTSELECTED FROM THE GROUP CONSISTING OF NON-ALKALINE METAL CHLORIDES ANDSULFATES.